Method of utilization of molten material as heat transferring medium



M. H ARVESON 2 Sheets-Sheet 1 Filed Jan. 3, 1955 TAR PIC-1.2.

OIL VAPDRS INVENTOR. MAI/RICE H ARI E150 B Y W a M ATTORNEY March 23, 1937.

METHOD OF UTILIZATION OF MOLTEN MATERIAL AS HEAT TRANSFERRING MEDIUM March 23, 1937. M. H. ARVESON 2,074,529 METHOD OF UTILIZATION OF MOLTEN MATERIAL AS HEAT TRANSFERRING MEDIUM Filed Jan. 5, 1955 2 Sheets-Sheet 2 v 99V n /397 yynssswa A/OdV/f v INVENTOR.

( i MAURICE HARM 55m 0* BY W ATTORNEY u.

Patented Mar. 23, 1937 UNITED STATES PATENT OFFICE METHOD OF UTILIZATION OF MOLTEN MATERIAL AS HEAT TRANSFERRING MEDIUM Application January 3, 1935, Serial No. 305

9 Claims.

' being treated is passed in heat-exchange relation ing temperatures, for the with the molten material, such as in processes involving the heating of hydrocarbon fluids to elevated temperatures for the production of motor fuel, such as gasoline.

While my invention is admirably suited to operations other than those involving the heating of hydrocarbon fluid, it will be particularly described in connection with heating hydrocarbon fluid to elevated temperatures, such as to crackproduction of motor fuel. I

Inheating of hydrocarbon fluid by passing it in heat-exchange relation with molten material, the molten material utilized is in fluid condition and at an elevated temperature in order to secure the desired heat transfer, whether direct or indirect to the hydrocarbon fluid being heated. To keep such material in molten condition it is necessary to subject it to a temperature at least as high as its melting point and preferably to a temperature above its melting point.

In shutting down an apparatus filled or partially filled with molten material at the desired temperature for the process, it has been custom ary to permit the material to solidify in the apparatus itself or to keep it in molten condition for a sufliciently long period to permit its removal to a suitable storage plant where it is permitted to solidify. solidification, of course, is due to the discontinuance of the application of heat to the molten material after a particular run has been completed.

Upon solidification of the material, it will be evident that the future use thereof is only possible when the material is again raised to a temperature at least as high as its melting point to again bring it to a molten state. This requires considerable time, not to mention expense, and if the material is stored in a storage plant separate from the apparatus used for carrying out the process, additional difliculties are experienced in pumping or otherwise returning this material to the apparatuswhere it is to be used.

In accordance with my invention, the disadvantages heretofore encountered in the handling of molten material in operations involving heat transfer from the molten material to the hydrocarbon fiuid being treated are obviated.

The expression molten material used throughout the specification and claims as a heat-transferring medium is intended to cover any salt or mixtures of various salts capable of having its melting point altered and suitable as a heattransferring medium to the fluid being heated, more particularly to a hydrocarbon fluid being heated to an elevated temperature.

My invention contemplates either in an operation where the molten material is maintained in a relatively stationary body or where the molten material is circulated from the heating zone therefor to the zone where it is utilized as a heattransferring medium, the maintaining of the material in a fluid or molten condition even after the heat normally applied thereto has been shut off.

In order to maintain the heat-transferring medium in a fluid or molten condition, my invention provides for the use of an extraneous fluid that changes the composition of the molten material so as to change its melting point, for example, changing the water content of a salt or salt mixture capable of being hydrated.

As contemplated by my invention, a'superatmospheric pressure is maintained within the apparatus used for carrying out the process by the pressure exerted on the extraneous fluid introduced into the molten material to insure that a suflicient quantity of the extraneous fluid is always retained in the molten material to keep the melting point thereof below the temperature which prevails in the heating apparatus. Consequently the quantity of extraneous fluid used to reduce the melting point of the molten material varies with the pressures prevailing in the heating apparatus, that is, as the pressure maintained on the molten material by the extraneous fluid decreases, less extraneous fluid is added thereto with at least a part thereof being retained in the molten material to insure that the melting point of the mixture of molten material and extraneous fluid will be below the temperature prevailing in the heating apparatus under the pressure conditions being maintained on the molten material. The same is true of temperature and. variations thereof likewise determine thequantity of extraneous fluid retained. Both temperature and pressure may, therefore, be varied to accomplish the desired cooling of the molten material without solidification thereof.

I have found that water or Water in the form of steam, which may be saturated or superheated, is an excellent extraneous fluid to use in order to insure that the melting point of a molten ma- 2 terial capable of being hydrated will be below the temperature prevailing in the heating apparatus. My invention contemplates introducing steam into the molten material to be absorbed, at least in part, thereby to reduce the melting point of the molten material. Moreover, the steam which is at a lower temperature than the molten material aids in the cooling thereof, especially at the beginning of the shut-down operation, which it is desired to accomplish with as much rapidity as is permissible; If more rapidv cooling is desired water without being heated to form steam may be used. The change produced upon the melting point of the molten material by the introduction of steam or water thereto depends of course on the amount thereof which combines with the molten material, the melting point thereof being lower with a greater content of water vapor. The steam or water vapor content, however, is dependent upon the steam pressure maintained within the apparatus and, therefore, with higher steam pressures it is possible to retain more water vapor or steam in the molten material and hence lower its melting point. It will be evident, therefore, that in accordance with my invention it is desirable to always maintain a high enough pressure on the molten material in order to retain suflicient water vapor or steam in solution or combination to insure that the melting point of the mixture or solution will be below the temperature prevailing in the apparatus. Consequently, as the temperatures and/or pressures prevailing in the apparatus retaining the molten as material are rprogressively decreased, the quantity of wate being introduced into the molten material is likewise progressively decreased, with the result that when the apparatus approaches normal temperature conditions, the molten material water mixture is in a fluid condition and easily handled. a

In carrying out my invention, it is preferable in the case of most salts to allow the molten material to gradually decrease in temperature after the source of heat and the hydrocarbon fluid being heated have been cut off until such time as the molten material approaches a temperature just above the melting point thereof in order that excessive pressures will be avoided. At this point the water or steam is introduced thereinto with the introduction thereof being continued from then on until the resulting mixture, which is in liquid condition, reaches atmospheric conditions or the condition under which'it is to be stored, noting the pressure and temperature relationship as an index to the condition of the molten material and therefore the degree of safety.

My invention will be further described in connection with the accompanying drawings in which:

Figure l is an elevational view of apparatus, partly in section, illustrating the application of my invention to a body of circulating molten material.

Figure 2 is an elevational view of apparatus, partly in section, illustrating the application of my invention to arelatively stationary body of molten material.

Figure 3 is a-reproduction of a plot on regular rectilineal coordinate paper for sodium hydroxide as an example of a salt showing the vapor pressure in pounds per square inch absolute plotted against temperature in degrees acreage Fahrenheit with the weight per cent of the sodium hydroxide as the parameter.

Referring to Figure 1, there is shown an apparatus wherein the molten material is continuously circulated during operation. The apparatus may comprise 'a furnace setting I having a suitable burner 2, of which a plurality may be employed, and a heating coil 3 posi-' tioned within the furnace setting. An enlarged reaction chamber 4 is suitably connected to the heating coil 8. As shown, the lower part of the reaction. chamber 4 is connected to the inlet of the heating coil 8 by means of a linev 5 and the upper part thereof is connected to the outlet of the heating coil by means of a line 6.

A body of molten material is maintained in the heating coil 3 and the reaction chamber 4,

' this material being circulated from the chamber 4, by means of a pump 1, to and through the heating coil 3 wherein it is heated to the desired elevated temperature by heat from the hot products of combustion produced by the burner 2. It will thus be evident that there is provided an arrangement whereby the body of molten material may be withdrawn from the reaction chamber, heated to the desired elevated temperature and then returned to the reaction chamber, at said elevated temperature, for use as a heat transferring medium.

During normal operation of the apparatus, the molten material therein is maintained at the desired elevated temperature and hydrocarbon fluid to be heated, preferably hydrocarbon vapors to be cracked, may be introduced under superatmospheric pressure into the reaction chamber 4 through a line B. The hydrocarbon vapors pass upwardly through the body of molten material in the reaction chamber 4 and are therein heated to the desired elevated temperature by direct contact with the molten material, thus cooling the molten material in this chamber and causing it to descend downwardly to the lower part of the reaction chamber.

The hydrocarbon fluid thus heated, preferably to an elevated cracking temperature, is conducted from the reaction chamber 4 through a line 9 controlled by a pressure reduction valve ii and passed to suitable equipment for further treatment, such as an evaporator and fractionator.

When it is desired to shut down the apparatus illustrated, solidification of the molten material pressure, which represents the steam vapor pressure within the apparatus, together with the temperature, determines the quantity of water vapor or steam retained by the molten material. Thus the introduction of steam is continued, decreasing in quantity and temperature with the dilution of the molten material and the lowering of pressure, the latter of which avoids over-dilution as the temperature falls, which results in shutting down the apparatus'rapidly without any solidification of the molten material therein. The

rate of introduction of steam into the body of molten material will depend upon the rate with which it is possible to cool the metal structure of the apparatus without setting up undue strain in any portion thereof. The steam unmixed with the molten material may be withdrawn through the line 9. The molten material-water mixture which is then in fluid condition under normal atmospheric condition may be kept in the apparatus for further use or withdrawn through a line l3 and passed to storage, if it is desired torepair the apparatus.

While I have shown steam being introduced into the molten material at only one point, it is to be clearly understood that regulated quantities of the steam may be introduced at a plurality of points. Thus, an additional stream of steam may be introduced into the body of molten material at an intermediate point in the reaction chamber 4. It will also be appreciated that in lieu of the type of apparatus shown in Figure 1, an appa- I In Figure 2 I have shown an apparatus for heat treatment of hydrocarbon fluid in which the molten material used as a heat-transferring medium is in a relatively stationary body. As shown, the apparatus may comprise a furnace setting 2|, provided with suitable burners 22, for producing hot products of combustion and a duct 23 for withdrawing the combustion products from the furnace setting. The furnace setting 2| encloses a reaction chamber 24 having a body of molten material 25 retained therein and maintained at the desired elevated temperature by the heat within the furnace settingj Hydrocarbon fluids to be raised to an elevated temperature, such as hydrocarbon vapors to be heated to cracking teinperat'ure, are introduced into a line 26 and passed through a line 21 into the body of molten material in the reaction chamber 24. The vapors in passing in direct contact with the body of molten material 25 are therein raised to the desired elevated temperature and are withdrawn through a line 28 fro-m which they are passed to an enlarged chamber 29 wherein separation of tar-like particles is effected. The enlarged chamber 29 may be provided with a tar draw-off line 3| and an overhead vapor line 32, having a pressure reduction valve 33, and connected to suitable other equipment, not shown, such as an evaporator and fractionator.

In carrying out my invention in an apparatus 5 of the type illustrated by Figure 2, steam, saturated or superheated, or water may be intro duced into a line 34 after the burners 22 and the supply of hydrocarbon fluid are shut off and passed through the line 21 into the body of molten material 25. The same general method of operation, asabove described, is carried out in connection with this type of apparatus, the quantity of steam and the temperature thereof being progressively decreased as the temperature and pressure of the molten material are decreased.

The steam not absorbed by the molten material in keeping it in a fluid condition passes through the line 28 into the chamber 29 from which it may be withdrawn through a line 35 controlled 7 by a pressure reduction valve 36.

, While I have shown passing the hydrocarbon fluid in direct contact with the body of molten material in both Figures 1 and 2, it is to be clearly understood that the hydrocarbon fluid may be passed in indirect heat exchange rela:

tion therewith. Thus a coil may be immersed in either or both of the reaction chambers 4 and 24 for conducting thev hydrocarbon fluid in indirect heat-exchange with the body of molten material. If a greater time of contactis desired in the apparatus shown, both the reaction chambers 4 and 24 may be provided with suitable internal baflles for causing the hydrocarbon fluid introduced thereinto to follow a tortuous path therein, thereby increasing the length of the path travelled and hence the time of contact between the hydrocarbon fluid and the moltefi material.

I have shown in Figure 3 the properties of a particular salt, namely sodium hydroxide, NaOH,

which are used to illustrate the principles of my invention.

Referring to this figure, it will be noted that the abscissa, as degrees F., has been plotted to as high as 700 F. and the ordinate, as vapor pressures expressed in pounds per square inch absolute, to above a thousand. It will be obvious that the salt used to effect the heating of hydrocarbon fluid and particularly the cracking of hydrocarbon vapors will be at a higher temperature, such as for instance from 950 to 1200 F., instead of 700 as shown in the plot. However, as aforementioned, the salt may be permitted to cool after any particular operation along with the apparatus until its temperature is just above the temperature of solidification.

By observing the plot shown in Figure 3, it will be noted that if the salt is at a temperature of approximately 600 F. and a steam vapor pressure of approximately 7 pounds per square inch absolute is maintained thereon, about 4.8% of the total molten bath will be water vapor retained by the sodium hydroxide. By gradually decreasing the temperature of the bath while at the same pressure, it will be further noticed that at a temperature of about 476 F., approximately 12.5% of the total sodium hydroxide water mixture is water.

In practicing my invention, it is preferable to decrease the temperature of the sodium hydroxide so that as the temperature decreases, the quantity of water retained by the sodium hydroxide is thereby increased to thus keep it in a fluid or molten condition. If desired, the pressure may be progressively decreased with the temperature. By observing the plot, it will be apparent that the temperature pressure conditions of the sodium hydroxide can be varied with the introduction of steam at the desired temperature to gradually but rapidly bring down the temperature of the salt with a sumcient quantity of water vapor therein to always insure that the melting point of the thus diluted salt will be below the temperature prevailing in the apparatus.

The line indicated as solid boundary on the plot shown in Figure 3 illustrates that in carrying out my invention it will be necessary to avoid certain temperaturepressure condition as otherwise the salt will become solid. For instance, with a pressure less than one pound per square inch absolute, it will be essential that the temperature of the bath of the moltenmaterials should not be permitted to fall from a high temperature to below 560 F. as otherwise the salt would become solid.

It will be apparent from a consideration of Figure 3 that it is possible to regulate the quantity of steam introduced into the sodium hydroxide with progressive decreasing ofthe temperature and/or pressure to bring the apparatus 4 down to normal atmospheric condition and have I the salt in a fluid or molten condition.

While I have chosen to specifically show the application of my invention with sodium by- 5 droxide, which has an exceptionally favorable solid range, it should be understood ,that other salts are just as applicable and some more applicable to the-heat treatment of hydrocarbon fluid, and particularly the cracking thereof. For .10 instance, calcium chloride which is particularly suited as a salt bath for the direct cracking of hydrocarbon fluid is an example of other salts. In the case of this salt, it has been found that higher steam pressure will be necessary to keep 15 it in molten condition. It might be mentioned in connection with calcium chloride that solidification takes place at about 75% by weight calcium chloride in water at a temperature of 347 F. and at a pressure of about 14.9 pounds per 20 square inch absolute. When using this salt, it will be necessary to maintain the pressure much higher than those for sodium hydroxide (NaOH) for the same temperatures.

My invention is not only applicable to the shut- 25 ting down of a unit, but also in the actual operation and starting up of the unit. For instance, in actual operation with salts or salt mixtures having a melting point higher than the temperature desired for the heat treatment of the 30 fluid under consideration, it will be apparent that water soluble salts with higher melting points may be made operable by maintaining quite small partial pressures of steam in the stream of hydrocarbon fluid'being heated to an elevated temperature, such as to cracking temperature. Thus, steam or water may be mixed with the hydrocarbon fluid entering the reaction chamberin either Figures 1 or 2 to thus reduce the melting point of the molten material. In starting up an operation in accordance with my invention, the salt which has been previously used and hydrated to lower its melting point is heated to the desired elevated temperature, with at least a part of the water vapor content being driven off. It will be thus apparent that all of the water vapor content may be driven OE and the salt raised to a temperature sumciently high to maintain it in fluid or meltedcondition.

While steam has been mentioned as a suitable 50 extraneous fluid, other fluids may be used. For example, ammonia may be used with certain salts, such as zincchloride and certain salts such as calcium nitrate (Ca(NOa)z), lithium nitrate (LiNOa), and others when indirect heat exchange 55 is used. Ammonia might be used continuously in said molten material bath where it is desired to prevent corrosion and decomposition of the salt due to hydrochloric acidor hydrogen sulphide when the stocks are being treated. It may also 60 be desirable in all cases oi molten bath cracking to maintain a supply of excess alkali or alkaliearth hydroxides to minimize corrosion in the system.

While my invention has been described with the heating of hydrocarbon fluid to an elevated temperature, such as cracking temperature, it is to be understood that it is also applicable to commercial processes wherein molten baths are used for direct heat transfer to stocks to be dehydrogenated, hydrogenated, polymerized or oxidized. From the foregoing, it will be apparent that the salt bath may be reduced from the operating temperature thereof during the actual processing of hydrocarbon fluids to normal-atmospheric tem- 75 peratures and yet be maintained in a fluid or aerasse molten condition. The principles of my invention are applicable to salts other than those specifically mentioned as the same type plot and the same method of operation may be used.

Obviously, many modifications in the apparatus and mode of operation may be made without departing from the spirit of the invention which is defined in its true scope in the appended claims.

I claim:

1. In an operation wherein hydrocarbon fluid is raised to an elevated temperature by passing it in heat exchange relation with a normally solid molten material maintained at an elevated temperature by applying heat thereto during the passage of hydrocarbon fluid in heat exchange relation therewith, the improvement in shutting down the operation that comprises discontinuing the application of heat to and the passage of hydrocarbon fluid in heat exchange relation with the molten material and thereafter continuously introducing an aqueous solution capable of lowering the melting point of the molten material at decreasing temperatures into contact with the molten material to thereby progressively decrease the temperature thereof and maintain it in molten condition throughout the drop in temperature and at substantially atmospheric conditions.

2. In an operation wherein hydrocarbon fluid is raised to an elevated temperature by passing it in heat exchange relation with a water-soluble and normally solid molten material maintained at an elevated temperature by applying heat thereto during the passage of hydrocarbon fluid in heat exchange relation therewith, the improvement in shutting down the operation that comprises discontinuing the application of heat to and the passage of hydrocarbon fluid in heat exchange relation with the water-soluble molten material and thereafter continuously introducing steam at decreasing temperatures into contact with the molten material to thereby progressively decrease the temperature thereof and maintain it in molten condition throughout the drop in temperature and at substantially atmospheric conditions.

3. In an operation wherein hydrocarbon fluid is raised to an elevated temperature bypassing it in heat exchange with normally solid molten material maintained in an apparatus at an elevated temperature by applying heat thereto during the passage of hydrocarbon fluid in heat exchange relation therewith, the improvement in shutting down the operation which comprises shutting off the source of heat and the passage of hydrocarbon fluid in heat exchange relation with the molten material, and thereafter introducing an aqueous solution capable of lowering the melting point of the molten material at a temperature lower than the temperature of the molten material into direct contact therewith to thereby cool the molten material and lower its melting point to a temperature belowthat prevailing in the apparatus during the entire shut-down period and to maintain it in molten state at substantially atmospheric conditions.

4. In an operation wherein hydrocarbon fluid is raised to an elevated temperature by passing it in heat exchange with a water-soluble and normally solid molten material maintained in an apparatus at an elevated temperature by applying heat thereto during the passage of hydrocarbon fluid in heat exchange relation therewith, the improvement in shutting down the operation which comprises shutting ofi the source of heat and the passage of hydrocarbon fluid in heat ex- 2,074,629 change relation with the molten material, and

thereafter introducing steam at a temperature lower than the temperature of the molten material into direct contact therewith to thereby cool the molten material and lower its melting point to a temperature below that prevailing in the apparatus during the entire shut-down period and to maintain it in molten state at substantially atmospheric conditions.

5. In an operation wherein hydrocarbon fluid is raised to an elevated temperature by passing it in heat exchange with a water-soluble and normally solid molten material maintained in an apparatus at an elevated temperature by applying heat thereto during the passage of hydrocarbon fluid in heat exchange relation therewith, the

improvement in shutting down the operation which comprises shutting off the source of heat and the passage of hydrocarbon fluid in heat exchange relation with the molten material, cooling the molten material to a temperature above the melting point thereof, thereafter introducing steam at a temperature lower than the temperature of the molten material into direct contact therewith to thereby cool the molten material and lower its melting point to a temperature below that prevailing in the apparatus during the entire shut-down period and to maintain it in molten state at substantially atmospheric conditions.

6. In an operation wherein hydrocarbon fluid is raised to an elevated temperature by passing it in heat exchange relation with normally solid molten material maintained at an elevated temperature by applying heat thereto during the passage of hydrocarbon fluid in heat exchange relation therewith, the improvement in shutting down the operation that comprises discontinuing the application of heat to and the passage of hydrocarbon fluid in heat exchange relation with the molten material, thereafter introducing an aqueous solution capable of lowering the melting point of the molten material into contact with said molten material and maintaining a superatmospheric pressure on the molten material by the pressure on the extraneous fluid and continuing the introduction of said extraneous fluid at decreasing temperatures to thereby decrease the temperature thereof and maintain it in molten condition throughout the drop in temperature and at substantially atmospheric conditions.

7. In an operation wherein hydrocarbon fluid is raised to an elevated temperature by passing it in heat exchange relation with normally solid molten material maintained at an elevated temperature by applying heat thereto during the passage of hydrocarbon fluids in heat exchange relation therewith, the improvement in shutting down the operation that comprises discontinuing the application of heat to and the passage of hydrocarbon fluid in heat exchange relation with the molten material, thereafter introducing an aqueous solution capable of lowering the melting point of the molten material into contact with said molten material and maintaining a superatmospheric pressure on the molten material'by the pressure on the extraneous fluid and progressively decreasing the pressure on the molten material while continuing the introduction of said extraneous fluid at decreasing temperatures to thereby decrease the temperature of the molten material and maintain it in molten condition throughout the drop in pressure and temperature and at substantially atmospheric conditions.

8. In an operation wherein hydrocarbon fluid is raised to an elevated temperature by passing it in heat exchange relation with a water-soluble normally solid molten material maintained at an elevated temperature by applying heat thereto during the passage of hydrocarbon fluid inheat exchange relation therewith, the improvement in shutting down the operation that comprises discontinuing the application of heat to and the passage of hydrocarbon fluid in heat exchange relation with the molten material, thereafter introducing steam into contact with said molten material and maintaining a superatmospheric pressure on the molten material by the pressure on the steam and progressively decreasing the pressure on the molten material while continuing the introduction of steam at decreasing temperatures to thereby decrease the temperature of the molten material and maintain it in molten condition throughout the drop in pressure and temperature and at substantially atmospheric conditions.

9. In an operation wherein a fluid is raised to an elevated temperature by passing it in heat exchange relation with normally solid molten material maintained at an elevated temperature by applying heat thereto during the passage of said fluid in heat exchange relation therewith, the improvement that comprises discontinuing the application of heat to and the passage of fluid in heat exchange relation with the molten material and thereafter introducing an aqueous solution at decreasing temperatures into contact with the molten material to thereby decrease the temperature thereof and maintain it in molten condition throughout the drop in temperature, and at substantially atmospheric conditions.

MAURICE H. ARVESON. 

